The present invention relates to a method and system for processing a thin-film semiconductor material, and more particularly to forming large-grained grain boundary-location controlled semiconductor thin films from amorphous or polycrystalline thin films on a substrate using laser irradiation and a continuous motion of the substrate having the semiconductor film being irradiated.
In the field of semiconductor processing, there have been several attempts to use lasers to convert thin amorphous silicon films into polycrystalline films. For example, in James Im et al., xe2x80x9cCrystalline Si Films for Integrated Active-Matrix Liquid-Crystal Displays,xe2x80x9d 11 MRS Bulletin 39 (1996), an overview of conventional excimer laser annealing technology is described. In such conventional system, an excimer laser beam is shaped into a long beam which is typically up to 30 cm long and 500 micrometers or greater in width. The shaped beam is stepped over a sample of amorphous silicon to facilitate melting thereof and the formation of grain boundary-controlled polycrystalline silicon upon the resolidification of the sample.
The use of conventional excimer laser annealing technology to generate polycrystalline silicon is problematic for several reasons. First, the polycrystalline silicon generated in the process is typically small grained, of a random micro structure (i.e., poor control of grain boundaries), and having a nonuniform grain sizes, therefore resulting in poor and nonuniform devices and accordingly, low manufacturing yield. Second, in order to obtain acceptable quality grain boundary-controlled polycrystalline thin films, the manufacturing throughput for producing such thin films must be kept low. Also, the process generally requires a controlled atmosphere and preheating of the amorphous silicon sample, which leads to a reduction in throughput rates. Accordingly, there exists a need in the field to generate higher quality thin polycrystalline silicon films at greater throughput rates. There likewise exists a need for manufacturing techniques which generate larger and more uniformly microstructured polycrystalline silicon thin films to be used in the fabrication of higher quality devices, such as thin film transistor arrays for liquid crystal panel displays.
An object of the present invention is to provide techniques for producing large-grained and grain boundary location controlled polycrystalline thin film semiconductors using a sequential lateral solidification process and to generate such silicon thin films in an accelerated manner.
At least some of these objects are accomplished with a method and system for processing an amorphous or polycrystalline silicon thin film sample into a grain boundary-controlled polycrystalline thin film or a single crystal thin film. The film sample includes a first edge and a second edge. In particular, using this method and system, a laser beam generator is controlled to emit a laser beam, and portions of this laser beam are masked to generate patterned beamlets, each of the beamlets having an intensity which is sufficient to melt the film sample. The film sample is continuously scanned at a first constant predetermined speed along a first path between the first edge and the second edge by the patterned beamlets. In addition, the film sample is continuously scanned at a second constant predetermined speed along a second path between the first edge and the second edge by the patterned beamlets.
In another embodiment of the present invention, the film sample is continuously translated in a first direction so that the fixed patterned beamlets continuously irradiate successive first portions of the film sample along the first path. The first portions are melted while being irradiated. In addition, the film sample is continuously translated in a second direction so that the fixed patterned beamlets irradiate successive second portions of the film sample along the second path. The second portions are melted while being irradiated. Furthermore, after the film sample is translated in the first direction to irradiate a next successive portion of the first path of the film sample, the first portions are cooled and resolidified, and after the film sample is translated in the second direction to irradiate a next successive portion of the second path of the film sample, the second portions are cooled and resolidified.
In yet another embodiment of the present invention, the film sample is positioned so that the patterned beamlets impinge at a first location outside of boundaries of the film sample with respect to the film sample. Also, the film sample can be microtranslated from the first location to a second location before the film sample is scanned along the second path, starting from the second location.
In a further embodiment of the present invention, after the film sample is scanned along the second path, the film sample is translated so that the beamlets impinge a third location which is outside the boundaries of the film sample microtranslated. Thereafter, the film sample can be stepped so that the impingement of the beamlets moves from the third location to a fourth location, the fourth location being outside of the boundaries of the film sample. Then, the film sample is maintained with the patterned beamlets impinging on the fourth location until the film sample stops vibrating and after the movement of the film sample ceases.
In another embodiment of the present invention, the film sample is continuously scanned in a first direction so that the fixed position beamlets scan the first path, and then in a second direction so that the fixed position beamlets scan the second path. After the film sample is translated in the first direction, it is continuously translated at the first constant predetermined speed in a second direction so that the patterned beamlets irradiate the first successive portions of the film sample along the second path, the second direction being opposite to the first direction. Then, the film sample is microtranslated so that the impingement of the beamlets moves from the first location to a second location, the second location being outside of boundaries of the film sample. Thereafter, the film sample is continuously translated at the second constant predetermined speed in a first direction so that the patterned beamlets irradiate second successive portions of the film sample along the second path until the beamlets impinge on the second location, the first direction being opposite to the second direction.